In northern Alberta are located what are popularly known as "tar sands" (and which probably would be more appropriately referred to as "bituminous sands") occasionally exposed at the surface of the ground but generally overlaid by soil to varying depths. The bituminous sands comprise a heavy percentage of quartz sand (say 80%), small amounts of clay, of the order of 5% water, and of the order of 15% bitumen by weight. The bituminous sand deposits are estimated to contain more than one million million barrels of oil.
For many years efforts have been made to recover the oil, and several processes have been proposed for the purpose. Many proposals have involved the mining of the sand and the extraction of the petroleum from the sand thereafter. The mining techniques and associated extraction techniques have generally involved intolerably high capital investments, energy expenditures, ecological damage, and extraction and refining costs.
Various methods have been proposed to extract the petroleum from the sands in situ without requiring the mining of the sands. Recognizing that most recoverable petroleum deposits have been located at much greater depths and therefore at higher temperatures and pressures than are to be found in the Alberta bituminous sands, engineers have proposed the artificial creation of similar conditions in the bituminous sands of Alberta. Alternating current applied across terminals embedded in a bituminous sand deposit for the purpose of the heating of a portion of the bituminous sand deposit by electrical conduction has not been successful, usually because of the formation of carbonized paths between the electrodes, limiting current flow to these paths. Since the thermal conductivity of the deposits is relatively low, the heating of paths of relatively small dimensions within a bituminous sand deposit has not been successful in raising the overall temperature of the deposit (or a sufficiently large volume thereof) to the desired value.
It has also been proposed to extract petroleum from underground bituminous sand deposits by forcing steam into the deposits and emulsifying the bitumen. The use of steam has required the generation at the surface of large amounts of process heat, and the problem exists that the steam cannot always be sufficiently confined to the particular portion of the deposit from which the petroleum is intended to be extracted, but rather tends to blow out of the deposit being treated. The high-temperature high-pH emulsions also tend to dissolve quartz and displace clay, with attendant flow and separation problems.
It has been proposed to burn a portion of the petroleum in situ so as to generate sufficient heat to raise the temperature of the remaining portion of the petroleum sufficiently to enable the petroleum to flow into suitable wells from which the petroleum may be extracted. Such methods have been generally unsatisfactory to date, and even if satisfactory would tend to waste a good deal of the stored energy of the underground petroleum through the burning process. Nuclear explosions have been advocated, but have not yet been experimentally tested, to realize much the same objective of increasing the heat and pressure within the underground deposit so as to enable at least a portion to be recovered. It is apparent however, that at least some of the petroleum would be carbonized by a nuclear explosion, and a significant portion or perhaps all of the petroleum that could be recovered in such a process (if the process were successful at all) would be contaminated by radioactivity.
In Colorado and other areas of the United States, there are large beds of oil shale. These oil shale deposits are sometimes exposed at the surface but generally are overlaid by other formations. Kerogen is entrapped within the oil shales. Again, the extraction of oil from the shales has not, to date, been commercially attractive because of the formidable problems encountered in separating oil from shale.
Finally, in many parts of North America, substantial underground lignite deposits exist. No economically attractive method is known for extracting the lignite. Mining has in the overwhelming majority of cases proved to be impossible or extremely hazardous because of the serious risk of explosion of oil or gas commonly found associated with the lignite deposits. The lignite deposits constitute a major potential hydrocarbon reserve, and a need exists for a safe and satisfactory method of recovery of the hydrocarbons.